1. Field of the Invention
The present invention relates to an electronic paper display device and a manufacturing method thereof, and more particularly, to an electronic paper display device capable of achieving excellent stability and uniformity of an image and the facilitation of contrast adjustment and a manufacturing method thereof.
2. Description of the Related Art
In recent years, changes in the way information is transferred and shared have been required to keep pace with an information society in which a new paradigm is required. In order to satisfy such a requirement, the development of electronic paper capable of being bent as a flexible display has been accelerated, and thus the technological development of electronic paper is now entering a commercially viable stage.
In comparison with an existing flat display panel, electronic paper offers lower manufacturing costs and superior energy efficiency in view of the fact that since electronic paper does not require background lighting or constant recharging, it can be driven even with very little energy. Also, electronic paper is very vivid and has a wide viewing angle. Moreover, electronic paper has a memory function allowing for the retention of characters even without power. These advantages allow for a wide range of electronic paper applications, such as an electronic book having a paper-like appearance and including moving illustrations, a renewable newspaper, a reusable paper display for a mobile phone, a disposable TV screen, or electronic wallpaper. Electronic paper therefore has huge market potential.
Proposed technical methods for the realization of electronic paper are divided into four approaches: a twist ball method allowing for the rotation of spherical particles having oppositely electrically charged upper and lower hemispheres of different colors by using an electric field; an electrophoretic method of keeping charged pigment particles mixed with oil in a microcapsule or a microcup and applying an electric field thereto or allowing charged particles to respond to the application of an electric field; a Quick Response-Liquid Powder Display (QR-LPD) method using a charged liquid powder; or a Cholesteric-Liquid Crystal Display (Ch-LCD) method using selective reflection of cholesteric liquid crystal molecules.
According to the twist ball method, a cell is filled with a transparent medium, and a twist ball having opposite electric charges and different colors, for example, a twist ball hemispherically colored black and white is disposed in the transparent medium. When voltage is applied to the twist ball, the twist ball rotates such that the hemisphere having a polarity opposite to that of the applied voltage is positioned toward the front side of a display according to direction of the applied voltage, and thus black or white can be displayed.
In this structure, however, since voltage is applied from upper and lower transparent electrodes disposed on the top and bottom of the cell, the twist ball rotates while allowing charged states to be balanced in a parallel manner according to the direction of the applied voltage. Accordingly, only two colors, i.e. black and white, are displayed, so there is a limitation in the display of contrast levels.